1. Field of the Invention
This invention relates generally to the preparation of cyclic organic compounds. In particular it relates to the thermal cleavage of unsaturated multi-cyclic ketones to produce cyclohexanone and other cleavage products including cyclohexene and cyclohexanol.
2. Prior Art Statement
References considered of particular pertinence are set forth below.
a. U.S. Pat. No. 3,574,757 (Collier) describes a process for hydrolytic cleavage of unsaturated bicyclic ketones which involves contacting a substantially anhydrous ketone with superheated steam and caustic. Although the starting material in this case is free of water, steam is added to the reaction mixture; part of this steam is consumed in the reaction which produces cyclohexanone. By way of contrast, the process of our invention uses no water whatsoever, and is thus a thermal rather than a hydrolytic cleavage. The hydrolytic cleavage of, for example, 2-(1-cyclohexenyl)cyclohexanone or 2-cyclohexylidenecyclohexanone proceeds in a manner such that one molecule of water reacts with one molecule of bicyclic ketone to yield two molecules of cyclohexanone. Surprisingly, it has now been found that cyclohexanone as well as other compounds are obtained when a thermal cleavage reaction in the absence of water is carried out according to the process of our invention. As in the hydrolytic cleavage reaction, the thermal cleavage reaction proceeds readily when the starting material is an essentially pure bicyclic ketone, or a mixture containing said bicyclic ketones such as the high boiling fraction obtained from the distillation of cyclohexanone and cyclohexanol. It is known that said high-boiling fractions contain a variety of multi-cyclic compounds such as 2-(1-cyclohexenyl)cyclohexanone, 2-cyclohexylidenecyclohexanone, and various other mutli-cyclic oxygenated compounds arising as condensation products of cyclohexanone or cyclohexanol. Thus, the chemical reaction of our process is different from that of U.S. Pat. No. 3,574,757, even though some operating conditions may be somewhat similar. Other references such as German patent Nos. 927,688 and 946,443, and Czech patent No. 95,459 describe variations of the hydrolytic cleavage process. PA1 b. Japanese Pat. No. 39-26965 describes a process for heat-treating of a mixture of multi-cyclic compounds containing unsaturated bicyclic ketones which involves heating the mixture in the presence of water and an inorganic acid catalyst at atmospheric pressure, and recovering cyclohexanone and cyclohexene from a portion of the mixture. By way of contrast, the process of our invention requires no water whatsoever and may be carried out without the use of a catalyst. Furthermore, it has been found that the addition of small amounts of water as low as three to four percent by weight of the starting material such as used in the examples of this reference gives significantly different results compared to conducting the cleavage reaction using a substantially dry starting material containing less than about one percent of water. Surprisingly, the cleavage reaction does not cease in the absence of water, but shifts from hydrolytic to thermal along with a corresponding shift in the amounts and percentages of cleavage products, especially cyclohexanone.
Thus, the cited references do not, whether alone or in combination, teach, suggest, or make obvious our invention, since the reactions therein are concerned with hydrolytic cleavage rather than thermal cleavage as in our process. Furthermore, the referenced art does not lead a person of ordinary skill in the art to predict with any degree of certainty the consequences of not having water present; experimental effort is essential.